Line drawing photoexposure device with image rotating means

ABSTRACT

A device for exposing lines on a photosensitive surface by means of a spot of light movable thereover comprises a source of light and an optical system for directing rays of light from the source onto the photosensitive surface to form a spot thereon. In the path of the light rays is a spot shape defining aperture, the projected spot being a real image of the aperture, and between the aperture and the photosensitive surface in a zone of nonparallel light is a &#39;&#39;&#39;&#39;non-restricted&#39;&#39;&#39;&#39; beam rotating system which is operable to rotate the projected light spot or image about the optical axis relative to the photosensitive surface to maintain a given axis of the spot perpendicular to the path of travel of the spot.

[ Nov. 19, 1974 LINE DRAWING PHOTOEXPOSURE DEVICE WITH IMAGE ROTATING MEANS [75] Inventors: Ronald B. Webster, Melrose;

Leonard G. Rich, West Hartford, both of Conn.

[73] Assignee: The Gerber Scientific Instrument Company, South Windsor, Conn.

[22] Filed: July 24, 1972 [21] Appl. No.: 274,797

3,582,203 6/1971 Cox 350/203 X 3,648,578 3/1972 Ritchie 95/12 3,688,655 9/1972 Klostermann 95/1 Primary Examiner-John M. l-loran Attorney, Agent, or Firm-McCormick, Paulding & Huber [5 7 ABSTRACT A devicev for exposing lines on a photosensitive surface by means of a spot of light movable thereover comprises a source of light and an optical system for directing rays of light from the source onto the photosensitive surface to form a spot thereon. In the path of the light rays is a spot shape defining aperture, the projected spot being a real image of the aperture, and between the aperture and the photosensitive surface in a zone of non-parallel light is a non-restricted beam rotating system which is operable to rotate the projected light spot or image about the optical axis relative to the photosensitive surface to maintain a given axis of the spot perpendicular to the path of travel of the spot.

6 Claims, 12 Drawing Figures PATENni z-iav 1 91974 SHEU 10? 4 FIG. 2

' PATENm, rm 1 91974 SHEET 2 (IF 4 PAI ENTEL, IISV I 9 I974 SIIEU 3 OF 4 FIG. 5

FIG. 7

LINE DRAWING PHOTOEXPOSURE DEVICE WITH IMAGE ROTATING MEANS BACKGROUND OF THE INVENTION This invention relates to a device for exposing lines on a photosensitive surface by means of a light spot moved thereover, and deals more particularly with such a device including a means for rotating the light spot relative to the photosensitive surface for the purpose of enabling a given axis of the spot to be maintained perpendicular to its path of travel.

A device of the general type with which this invention is concerned is shown by prior US. Pat. No. 3,330,182. In the device of this latter patent a table supports a sheet of photosensitive material and a photoexposure device which produces a spot of light directed onto the photosensitive material is supported for movement in a plane above the table. The photoexposure device is movable in any direction in its plane of movement so as to be able to trace any desired line on the photosensitive surface. The shape of the light spot is provided by an aperture, with the spot being a real image of the aperture, which may be one selected from a group of apertures carried by an aperture wheel. In the device of the above patent a circular aperture may be used to define the shape of the spot, and since a circular spot is symmetrical above its axis, there is no need for rotating such spot as it is moved in different directions over the photosensitive surface.

In some cases, however, it is desirable to expose lines on a photosensitive surface by means of a square or rectangular light spot or some other type of light spot having an unsymmetrical shape. For example, in cartography work it is often desirable to generate two parallel lines to represent a road or railroad track and such parallel lines may be drawn simultaneously by using a light spot consisting in turn of two separate sub-spots spaced from one another. When using an unsymmetrically shaped spot with a projecting mechanism which moves in all directions relative to the photosensitive surface being exposed, it is desirable and often necessary to maintain a given axis of the spot shape perpendicular to the path of travel of the spot. As an example, when using a spot consisting of two spaced sub-spots for the purpose of simultaneously exposing two spaced parallel lines the spot should be oriented in such a manner that the line passing through the two sub-spots is maintained perpendicular to the path of travel of the spot at all times.

Therefore, in photoexposure devices utilizing unsymmetrical spot shapes capable of being moved in all directions over the surface being exposed some means should be provided for rotating the spot relative to the photosensitive surface to maintain a desired orientation of the spot shape relative to its path of travel. Prior US. Pat. No. Re.'27,265 shows a photoexposure device with such a spot rotating means wherein the rotating means comprises essentially a clove prism. The use of a'dove prism in such a device, however, has certain disadvantages, and the object of this invention is to provide an improved type of photoexposure device including an image rotating means. In particular, a dove prism when used in a photoexposure device of the type in question for the purpose of rotating the projected spot is restricted to use only in a zone of parallel light rays. Therefore, it is necessary to combine with the dove prism a collimating lens or lens system for providing a zone of parallel light rays within which the dove prism may work. Also, dove prisms produce certain aberrations or distortions of the image passing therethrough, particularly astigmatic and chromatic aberrations.

As used herein the term zone of parallel light rays is used to refer to a zone in an optical imaging system wherein all of the rays originating from any given point on the object are parallel to one another. The term zone of non-parallel light rays is used to refer to a zone in an optical imaging system wherein all of the light rays originating from any given point on the object are not parallel but instead are either diverging or converging relative to one another. The term restricted image rotator refers to an image rotating means, such as a dove prism, which is effective, that is does not cause dispersion of the image forming rays, only when used in a zone of parallel light rays. The term nonrestricted image rotator refers to an image rotating means which is not restricted to use in a zone of parallel light and which instead is effective in either a zone of parallel light or a zone of non-parallel light.

As an image rotating means, the photoexposure line drawing device of the present invention uses a nonrestricted image rotator located in a zone of nonparallel light thereby avoiding the need for a collimating lens or lens system. This in turn avoids the cost and design complexities involved in the addition of a collimating lens or lens system to the imaging system and also avoids the additional aberrations such a lens system adds to the projected image. The non-restricted image rotator is in the form of either a mirror assembly or a prism providing an odd number of reflecting surfaces which are rotatable in unison about a given straight line colinear with the optical axis of the rays entering the assembly. When a prism is used as the image rotator, the prism is one, such as a Pechan or reversion prism, which has its entrance and exit surfaces arranged perpendicular to the optical axis. Among other things, this-arrangement avoids astigmatic and chromatic abberrations. When mirrors are used to form an image rotator, they also avoid these aberrations. Additionally, when mirrors are used, the reflecting surfaces are preferably front surface mirrors so that little or no internal energy absorption occurs as the light rays pass through the assembly thereby avoiding heating of the assembly and allowing it to be used with high energy light sources. Still further, the use of mirrors to form an image rotator means that the various angles by which the light path is bent as it passes through the rotator are not limited to the internal refractance angle of glass or other prism material. Therefore, the mirrors may be arranged at a wide variety of interrelated angles to best suit the remainder of the imaging system with which it is used.

SUMMARY OF THE INVENTION This invention resides in a line drawing photoexposure device which projects a spot of light onto a photosensitive surface to expose a line on such surface as the spot is moved thereover. In addition to a source of light, a means for directing the light rays from the source onto the photosensitive surface to form a spot and a means. in the path of the light rays for defining the shape of the spot, the device includes an image rotator in the path of the light rays between the spot shape defining means and the photosensitive surface for rotating the spot to vary its orientation relative to the surface for the purpose of enabling a given axis of the spot to be maintained perpendicular to its path of travel over the photosensitive surface. This image rotator is of the non-restricted type and is located in a zone of nonparallel light rays. It may consist of either a mirror assembly or a prism providing three, or other odd number of, planar reflecting surfaces for deflecting the light rays passing through the assembly in such a manner that as the light rays pass through the assembly their optical axis is first directed away from and then back to a given straight line. When the image rotator is a prism, the entrance and exit surfaces of the prism are arranged perpendicular to the optical axis.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a mechanism, constructed in accordance with the present invention, for exposing lines on a photosensitive surface.

FIG. 2 is a side elevational view of the photoexposure device of the mechanism of FIG. 1 for projecting a spot of light onto the photosensitive surface, part of the housing of the device being broken away to show further details and part of the device within the housing being shown somewhat schematically.

FIG. 3 is a front elevational view of the lower portion of the projecting device of FIG. 2 shown with the housing removed.

FIG. 4 is a side view, partly in elevation and partly in section, of the portion of the projecting device shown in FIG. 3.

FIG. 5 is a view taken generally on the line 5-5 of FIG. 4.

FIG. 6 is a sectional view taken generally on the line 6-6 of FIG. 5.

FIG. 7 is a fragmentary view taken generally on the lines 7-7 of FIG. 5.

FIG. 8 is a fragmentary view taken generally on the line 8-8 of FIG. 6.

FIG. 9 is a view showing one of the mirror members of the mirror assembly of FIG. 6 rotated 90 from its FIG. 6 position.

FIG. 10 is a view similar to FIG. 5 but shows another embodiment of this invention using a Pechan prism as the image rotator.

FIG. 11 is a sectional view taken generally on the line l111ofFIG. 10.

FIG. 12 is a view similar to FIG. 6 but shows another embodiment of this invention using a reversion prism as the image rotator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Considering first FIG. 1, this figure shows a graphic artwork producing system embodying this invention and consisting of a photoexposure apparatus 10 and an associated automatic controller 12. The apparatus 10 is in large part generally similar to a conventional X-Y plotter and includes a table defining a surface 14 for holding a piece of photosensitive material 16 having an upwardly facing light sensitive surface 17 on which lines are to be exposed, one such line being shown, for example, at 18. A photoexposure device 20 is supported for movement above the supporting surface 14 in a plane parallel thereto. The means for so supporting the device 20 includes a carriage 22 straddling the table and movable in the illustrated X coordinate direction by a lead screw 24 driven by an associated motor 26. The device 20 in turn is attached to or part of a subcarriage movable in the illustrated Y coordinate direction along the main carriage 22 and is driven in such movement by a lead screw 28 powered by an associated motor 30. The drive motors 26 and 30 are energized by appropriate signals from the controller 12 to cause the photoexposure device 20 to be driven simultaneously in the X and Y coordinate directions so as to follow any desired line on the photosensitive material 16. The controller 12 also supplies other signals to the device 20 for controlling its operation as hereinafter described.

The overall construction of the photoexposure device 20 is shown in FIG. 2. Except for the inclusion of an image rotator for rotating the projected spot to vary its orientation relative to the light sensitive surface 17 this mechanism is similar to that shown by FIGS. 2 to 5 of prior US. Pat. No. 3,330,182, and reference may be made to said patent for further details. In essence, however, the photoexposure device 20 includes a light source 32 which may be either an arc lamp or an incandescent lamp. By a convex mirror 34 and a series of lenses 36, 38 and 40 light rays from this sourceare first caused to converge at a point 42 to produce a real image of the light source. At or near thispoint 42 is a variable density filter disc 44 which is driven by a motor 46, in response to signals related to the speed of the light spot relative to the photosensitive surface 17, to vary the intensity of the light rays passing beyond the filter disc in accordance with the speed of the light spot to maintain proper exposure of the photosensitive surface at all light spot speeds.

Beyond the filter disc 44 the light rays are first deflected downwardly by a mirror 46 and then pass through a condensing lens 48. Below the condensing lens 48 is an aperture wheel 50 carrying a plurality of apertures of different shapes and sizes arranged in an annular array, any one of which apertures may be positioned in operative position by indexing the aperture wheel about itscentral axis. A motor 52 performs this indexing function. The aperture wheel 50 is similar to the aperture wheel 98 shown and described in the aforesaid US. Pat. No. 3,330,182 which describes such wheel in detail. In any event, it will be understood that the one aperture positioned in operative position below the condensing lens 48 serves to define the shape of the spot projected onto the light sensitive surface 17 and such shape, in addition to possibly being circular, may

possibly be a square, a rectangle, two spaced sub-spots or other non-circular shape. Also, it will be understood that the aperture wheel 50 is shown by way of example only and, if desired, various other means may be used to provide a spot shaping aperture. Below the aperture wheel 50 is a projecting lens 54. This lens may be either a single lens or a lens system, but for convenience is referred to herein as a lens. The lens 54 has the operative aperture of the aperture wheel 50 as its object and the photosensitive surface 17 as its, image plane so that a light spot 53 is formed on the photosensitive surface which is in actuality a real image of the aperture. A motorized shutter mechanism 56 is located above the projecting lens system 54 for interrupting the light rays passing to the projecting lens system 54 to turn the light spot on and off as desired.

From the foregoing, it will be understood that the projecting lens 54, the operative aperture of the aperture wheel 50, and the photosensitive surface 17 form a simple optical imaging system for forming an image of the aperture (the object) on the photosensitive surface. Between the aperture and the lens is a first zone of non-parallel light in which the rays emanating from any given point of the aperture are diverging, and between the lens and the photosensitive surface is a second zone of non-parallel light in which the rays emanating from any given point on the aperture are converg- In addition to the above-described elements of the photoexposure device 20, such device further includes a non-restricted image rotator. This image rotator may be located in either of the two above-mentioned zones of non-parallel light, but preferably, and as shown, is located in the first zone between the aperture and the lens. The image rotator is indicated generally at 58 in FIG. 2 and operates, in response to its own rotation, to rotate the light rays passing therethrough about the optical axis to vary the angular orientation of the light spot 53 relative to the photosensitive surface 17.

FIGS. 5 to 9 show in more detail the construction and operation of the non-restricted image rotator 58. Turning first to FIGS. 3 and 4, the illustrated image rotator comprises a mirror assembly 60 located within and carried by a barrel member 62. This barrel member 62 is supported for movement about its vertical central axis 64 by two bearings 66, 66 located at opposite ends thereof and working between the barrel member and a part 68 of the main frame of the device 20. Fixed to the lower end of the barrel member is an annular gear 70 which is driven through an idler gear 72 by a pinion 74 fixed to the output shaft of a motor 76. The motor 76 is controlled by signals supplied thereto over the line 78 from the associated automatic controller 12 and is mounted on a bracket 80 forming part of the main frame. I

Turning next to FIGS. 5 and 6 for a more detailed consideration of the mirror assembly 60, the line 82 in FIG. 6 represents the optical axis of the light rays passing through the mirror assembly, and the barrel member 62 has its axis of rotation 64 aligned with those portions of the optical axis entering and leaving the mirror assembly. The mirror assembly includes three planar reflecting surfaces which deflect the light rays passing therethrough in such a manner that their optical axis 82 is first deflected away from and then back to the center line 64, and as a result of this deflection when the reflecting surfaces are rotated in unison about the center line 64 the projected image or light spot 53 is also rotated about such center line. Furthermore, although the light rays entering the assembly and coming from any given point of the aperture enter at different angles to one another, they will leave the assembly at the same relative angles to one another, the mirrors therefore not dispersing the rays and destroying the image despite being located in a zone of non-parallel light. That is, the mirror assembly 60 is a non-restricted image rotator.

The three reflecting surfaces of the illustrated mirror assembly 60 are indicated, respectively, at 84, 86 and 88. All three of these surfaces are front surface mirrors by which is meant that they are specular surfaces formed on the exterior of the bodies defining them. Therefore, the light rays reflected by these surfaces do not pass through any part of the mirror bodies and are not subject to any refractance or internal energy absorption problems. The two reflecting surfaces 84 and 88 are formed on a single mirror body and the reflecting surface 86 is formed on another mirror body 92. The first reflecting surface 84 is arranged with its surface at an inclined angle to the center line 64, the second reflecting surface 86 is spaced from and parallel to the center line 64 and the third reflecting surface 88 is inclined to the center line 64 by the same angle as the surface 84 but in the opposite direction, all as shown in FIGS. 5 and 6.

The two lines a and b in FIG. 6 represent two light rays passing through the mirror assembly 60 and spaced on opposite sides of the optical axis 82 as viewed in FIG. 6. In tracing the passage of these light rays through the mirror assembly, it will be noted that they are first reflected from the surface 84 to the surface 86 then to the surface 88, and then downwardly towards the photosensitive surface. As they leave the mirror assembly, however, the rays a and b are reversed relative to the optical axis 82 in comparison to the positions occupied when entering the mirror assembly. Therefore, it will be understood that the mirror assembly, as to rays located in a common plane perpendicular to all three reflecting surfaces, turns such rays about the center line 6.4.

Assume now that the barrel member 62 is rotated 90, in the counterclockwise direction looking downwardly onto the barrel member in FIG. 6, from the FIG. 6 position to in turn rotate the three reflecting surfaces 90 about the center line 64. FIG. 9 shows the two reflecting surfaces 84 and 88 of the mirror body 90 at this new position and also shows the same two rays a and b of FIG. 6 the common plane of which is now parallel to the plane of the reflecting surface 86. From consideration of FIG. 6, it will be apparent that as the light rays a and b now pass through the mirror assembly no rotation of them about the center line 64 occurs. Therefore, it will be understood that as the mirror assembly rotates through 90 about the center line 64 the light rays passing therethrough are rotated 180 about the same line to likewise rotate the projected light spot 180 relative to the photosensitive surface 17. Accordingly, in order to maintain a given axis of the projected light spot 53 perpendicular to the path of travel of the light spot, the mirror assembly may be rotated by an gular amounts equal to one-half the angular change of direction of the line of travel of the light spot relative to the photosensitive surface 17, and in response to such changes in the direction of the line of travel of the light spot. The signals provided to the motor 58 from the controller 12 are programmed to be of such a nature as to achieve this desired rotation of the mirror assembly.

In order that the optical axis 82 of the light rays departing from the mirror assembly be aligned with the central line 64, it is necessary that the reflecting surfaces 84, 86 and 88 be accurately positioned in the barrel member 62. To achieve this accurate positioning of the reflecting surfaces they are preferably so mounted as to allow manual adjustment of their positions in various directions while in place in the projecting mechanism. To permit this type of adjustment, the two mirror bodies 90 and 92 in the illustrated device are both fixed to a first support member 94. This first support member is in turn adjustably attached to an L-shaped second support member 96. The member 96 includes three adjustment screws 98, 98, shown best in FIGS. 5 and 7, which have inner ends bearing against, and received in correspondingly shaped recesses in, the first support member 94 so that the contact of the member 94 with the ends of the screws determines the position of the member 94. The member 94 is maintained resiliently in contact with the ends of the screws 98, 98 by a screw 100 threaded into the member 94, passing loosely through the member 96 and having a compression spring 102 working between its head and the member 96 as shown in FIG. 5. Therefore, it will be understood that by adjusting the three screws 98, 98 the member 94 may be moved along a vertical line, as viewed in FIG. 5, toward and away from the center line 64 and may also be tilted relative to such center line.

The second support member 96 is attached to the barrel member 62 by three adjustment screws 104, 104 which are threaded into the barrel member and which have their inner ends resiliently held in engagement with corresponding recesses in the member 96 by another screw 106 passing loosely through the barrel member, threaded into the member 96 and having a spring 108 working between the barrel member 62 and the head of the screw 106. By adjustment of the screws 104, 104 the second member 96 may be moved along a horizontal line, as viewed in FIG. 5, toward and away from the center line 64 and may also be tilted relative to the center line. Therefore, by combined adjustment of the adjustment screws 98, 98 and 104, 104 the reflecting surfaces 84, 86 and 88 may be quickly and easily brought into proper position relative to the center line 64.

In addition to the image rotator comprising a set of mirrors, such as, for example, described above, the rotator also may, in accordance with the broader aspects of this invention, be provided by a prism wherein the light rays are reflected from internal surfaces of the prism either by total refractance or by reflectance from silvered surfaces. To obtain rotation of the projected image, it is necessary that the light passing through the rotator be reflected an odd number of times, and a number of different prisms under certain conditions are capable of performing this function. As mentioned above, it is known to use a dove prism in a line drawing photoexposure device for achieving image rotation. However, such a prism requires collimated light. As part of this invention, it has been found that other prisms may be used as image rotators and may be located in zones of non-parallel light without distorting the projected image. Such prisms, as mentioned above, are referred to herein as non-restricted prisms. In particular, Pechan prisms and reversion prisms have been found to serve particularly well as non-restricted image rotators. In both of the latter kinds of prisms, the entrance and exit faces are perpendicular to the optical axis and this has been found to be important to the capability of the prism to perform satisfactorily in a nonparallel light zone.

Referring to FIGS. 10 and 11, these figures show the image rotating mechanism of a photoexposure device which otherwise may be taken to be identical to the photoexposure device 20 described above, FIGS. 10 and 11 corresponding generally to FIGS. and 6 of the previously described embodiment. In FIGS. 10 and 11, parts which are similar to those shown in FIGS. 5 and 6 have been given the same reference numerals as in the latter figures and need not be redescribed. The image rotating means of FIGS. 10 and 11 is similar to that of FIGS. 5 and 6 except for using as the basic image rotator a Pechan prism in place of the mirror assembly 60. The Pechan prism 110 is fixed, as by cement, to a plate 112 which takes the place of the L- shaped bracket 94 of FIG. 5. Otherwise, the mounting means and the means for rotating the prism 110 are the same as that for the mirror assembly 60 of FIG. 5. In FIG. 11, the dotted line shows the path of the optical axis of the light rays in passing through the Pechan prism 110. The prism has an entrance face 116 which is perpendicular to the optical axis 114 and an exit face 118 which is also perpendicular to the optical axis. The Pechan prism actually consists of two separate bodies 120 and 122 which are separated from one another along the plane 124, with the surfaces 126 and 128 being silvered. Therefore, light rays in passing through the prism are reflected five times.

FIG. 12 is similar to FIG. 11 but shows a reversion prism 130 used as the basic image rotating member. In this figure, all of the parts are the same as those shown in FIGS. 10 and 11 except for the reversion prism 130 of FIG. 12 being substituted for the Pechan prism 110 of FIGS. 10 and 11. Therefore, the parts of FIG. 12 which are similar to corresponding parts of FIGS. 10 and 11 have been given the same reference numerals as in FIGS. 10 and 11 and need not be further described. In considering FIG. 12, the dotted line 132 represents the path taken by the optical axis in passing through the reversion prism 130 and it will be noted that such path is reflected three times in passing through the prism. Also, the prism has entrance and exit surfaces 134 and 136 respectively which are arranged perpendicular to the optical axis.

We claim:

1. A photoexposure mechanism for exposing lines on a photosensitive surface by means of a light spot moved thereover, said mechanism comprising means defining a supporting surface for supporting a piece of material having a photosensitive surface, and a photoexposure device supported for movement relative to said supporting means in a plane generally parallel to said supporting surface, said photoexposure device comprising an aperture, means for illuminating said aperture, and an optical imaging system for forming an image of said aperture on said photosensitive surface which image is a substantially undistored optical reproduction of said aperture and constitutes the aforesaid spot which is moved over said photosensitive surface to expose lines thereon as a result of movement of said photoexposure device relative to said supporting surface, the path of light rays through said optical imaging system including at least one zone of non-parallel light rays, and an image rotator capable of rotating said non-parallel light rays, said image rotator being located in said zone of non-parallel light rays for rotating said image relative.

to said photosensitive surface, said imaging system comprising a lens located between said aperture and said photosensitive surface and said image rotator being located between said aperture and said lens, said image rotator comprising a mirror assembly defining an odd number of planar reflecting surfaces encountered successively by a light ray passing through said assembly and arranged to deflect such a ray traveling along the optical axis of said rays firstaway from and then eventually back to a straight line colinear with said optical axis as said optical axis enters said mirror assembly, and means for rotating said mirror assembly about said given straight line, said photoexposure device also including a first support member to which said mirror assembly is fixed, a second support member, means attaching said first support member to said second support member and permitting said first support member to be manually adjusted relative to said second member to shift said first support member toward and away from said given straight line along a first line perpendicular to said straight line and to vary the inclination of said first support member relative to said straight line in the plane defined by said first line and said given straight line, a third support member, means attaching said second support member to said third support member and permitting said second support member to be manually adjusted relative to said third member to shift said second support member toward and away from said given straight line along a second line perpendicular to both said given straight line and first line and to vary the inclination of said second support member relative to said given straight line in the plane defined by said second line and said given straight line, and a main frame, said means for rotating said mirror assembly including means mounting said third support member to said main frame for rotation relative to said main frame about said given straight line.

2. A photoexposuremechanism as defined in claim 1 further characterized by said third support member being a barrel member having its axis generally aligned with said given straight line, and two bearings located respectively at opposite ends of said barrel member for rotatably supporting said barrel member relative to said main frame, said first support member, said second support member and said mirror assembly being located within said barrel member generally between said two bearings.

3. A photoexposure mechanism for exposing lines on a photosensitive surface by means of a light spot moved thereover, said mechanism comprising means defining a supporting surface for supporting a piece of material having a photosensitive surface, and a photoexposure device supported for movement relative to said supporting means in a plane generally parallel to said supporting surface, said photoexposure device comprising an aperture, means for illuminating said aperture, and an optical imaging system for forming an image of said aperture on said photosensitive surface which image is a substantially undistorted optical reproduction of said aperture and constitutes the afore-said spot which is moved over said photosensitive surface to expose lines thereon as a result of movement of said photoexposure device relative to said supporting surface, the path of light rays through said optical imaging system including at least one zone of non-parallel light rays, and an image rotator capable of rotating said non-parallel light rays, said image rotator being located in said zone of non-parallel light rays for rotating said image relative to said photosensitive surface, said image rotator comprising a Pechan prism having a plurality-of surfaces fixed relative to one another for reflecting said light rays in such a manner that as said light rays pass therethrough their optical axis is first reflected away from and then eventually back to a given straight line, and means for rotating said Pechan prism about said given straight line, said Pechan prism having entrance and exit faces both of which faces are arranged perpendicular to the optical axis of the entering and departing light rays.

4. A photoexposure mechanism for exposing lines on a photosensitive surface by means of a light spot moved thereover, said mechanis m comprising means defining a supporting surface surface, and a photoexposure device supported for movement relative to said supporting means in a plane generally parallel to said supporting surface, said photoexposure device comprising an aperture, means for illuminating said aperture, and an optical imaging system for forming an image of said aperture on said photosensitive surface which image is a substantially undistorted optical reproduction of said aperture and constitutes the afore-said spot which is moved over said photosensitive surface to expose lines thereon as a result of movement of said photoexposure device relative to said supporting surface, the path of light rays through said optical imaging system including at least one zone of non-parallel light rays, and an image rotator capable of rotating said non-parallel light rays, said image rotator being located in said zone of non-parallel light rays for rotating said image relative to said photosensitive surface, said image rotator comprising a reversion prism having a plurality of surfaces fixed relative to one another for reflecting said light rays in such a manner that as said light rays pass therethrough their optical axis is first reflected away from and then eventually back to a given straight line, and means for rotating said reversion prism about said given straight line, said reversion prism having entrance and exit faces both of which faces are arranged perpendicular to the optical axis of the entering and departing light rays.

5. A photoexposure mechanism for exposing lines on a photosensitive surface by means of a light spot moved thereover, said mechanism comprising means defining a supporting surface for supporting a piece ofmaterial having a photosensitive surface, and a photoexposure device supported for movement relative to said supporting means in a plane generally parallel to said supporting surface, said photoexposure device comprising an aperture, means for illuminating said aperture, and an optical imaging system for forming an image of said aperture on said photosensitive surface which image is a substantially undistorted optical reproduction of said aperture and constitutes the afore-said spot which is moved over said photosensitive surface to expose lines thereon as a result of movement of said photoexposure device relative to said supporting surface, the path of light rays through said optical imaging system including at least one zone of non-parallel light rays, and an image rotator capable of rotating said non-parallel light rays, said image rotator being located in said zone of non-parallel light rays for rotating said image relative to said photosensitive surfaces, said image rotator comprising a prism having a plurality of surfaces fixed relative to one another for reflecting said light rays in such a manner that as said light rays pass thereth'rough their optical axis is first reflected away from and then eventually back to a given straight line, and means for rotating said prism about said given straight line, said prism having entrance and exit faces both of which faces are arranged perpendicular to the optical axis of the entering and departing light rays, said photoexposure device including a first support member to which said prism is fixed, a second support member, means attaching said first support member to said second support member and permitting said first support member to be manually adjusted relative to said second member to shift said first support member toward and away from said given straight line along a first line perpendicular to said straight line and to vary the inclination of said first support member relative to said straight line in the plane defined by said first line and said given straight line, a third support member, means attaching said second support member to said third support member and permitting said second support member to be manually adjusted relative to said third member to shift said second support member toward and away from said given straight line along a second line perpendicular to both said given straight line and said first line and to vary the inclination of said second support member relative to said given straight line in the plane defined by said second line and said given straight line, and a main frame,

said means for rotating said prism including means mounting said third support member to said main frame for rotation relative to said main frame about said given straight line.

6. A photoexposure device as defined in claim 5 further characterized by said third support member being a barrel member having its axis generally aligned with said given straight line, and two bearings located respectively at opposite ends of said barrel member for rotatably supporting said barrel member relative to said main frame, said first support member, said second support member and said prism being located within said barrel member generally between said two bearings.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT r40. 3,848, 520

DATED November 19, 1974 INVENTOR( I Ronald B. Webster and Leonard G. Rich it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

C01. 1, line 28, "above" should read about- C01. 8, line 46, "undistored" should read --undistorted- Col. 10, line 4, after "surface" (first occurrence) insert -for supporting a piece of material having a photosensitive-- Signed and sealed this =Oth day of June 1.975.

( S EAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT r40. 1 3,848, 520

DATED November 19, 1974 INVE O 1 Ronald B. Webster and Leonard G. Rich it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

C01. 1, line 28, "above should read --about- Col. 8, line 46, "undistored" should read -undistorted-- Col. 10, line 4, after "surface" (first occurrence) insert -for supporting a piece of material having a photosensitive-- Signed-and sealed this 30th day ofrJune 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks 

1. A photoexposure mechanism for exposing lines on a photosensitive surface by means of a light spot moved thereover, said mechanism comprising means defining a supporting surface for supporting a piece of material having a photosensitive surface, and a photoexposure device supported for movement relative to said supporting means in a plane generally parallel to said Supporting surface, said photoexposure device comprising an aperture, means for illuminating said aperture, and an optical imaging system for forming an image of said aperture on said photosensitive surface which image is a substantially undistored optical reproduction of said aperture and constitutes the aforesaid spot which is moved over said photosensitive surface to expose lines thereon as a result of movement of said photoexposure device relative to said supporting surface, the path of light rays through said optical imaging system including at least one zone of non-parallel light rays, and an image rotator capable of rotating said non-parallel light rays, said image rotator being located in said zone of non-parallel light rays for rotating said image relative to said photosensitive surface, said imaging system comprising a lens located between said aperture and said photosensitive surface and said image rotator being located between said aperture and said lens, said image rotator comprising a mirror assembly defining an odd number of planar reflecting surfaces encountered successively by a light ray passing through said assembly and arranged to deflect such a ray traveling along the optical axis of said rays first away from and then eventually back to a straight line colinear with said optical axis as said optical axis enters said mirror assembly, and means for rotating said mirror assembly about said given straight line, said photoexposure device also including a first support member to which said mirror assembly is fixed, a second support member, means attaching said first support member to said second support member and permitting said first support member to be manually adjusted relative to said second member to shift said first support member toward and away from said given straight line along a first line perpendicular to said straight line and to vary the inclination of said first support member relative to said straight line in the plane defined by said first line and said given straight line, a third support member, means attaching said second support member to said third support member and permitting said second support member to be manually adjusted relative to said third member to shift said second support member toward and away from said given straight line along a second line perpendicular to both said given straight line and first line and to vary the inclination of said second support member relative to said given straight line in the plane defined by said second line and said given straight line, and a main frame, said means for rotating said mirror assembly including means mounting said third support member to said main frame for rotation relative to said main frame about said given straight line.
 2. A photoexposure mechanism as defined in claim 1 further characterized by said third support member being a barrel member having its axis generally aligned with said given straight line, and two bearings located respectively at opposite ends of said barrel member for rotatably supporting said barrel member relative to said main frame, said first support member, said second support member and said mirror assembly being located within said barrel member generally between said two bearings.
 3. A photoexposure mechanism for exposing lines on a photosensitive surface by means of a light spot moved thereover, said mechanism comprising means defining a supporting surface for supporting a piece of material having a photosensitive surface, and a photoexposure device supported for movement relative to said supporting means in a plane generally parallel to said supporting surface, said photoexposure device comprising an aperture, means for illuminating said aperture, and an optical imaging system for forming an image of said aperture on said photosensitive surface which image is a substantially undistorted optical reproduction of said aperture and constitutes the afore-said spot which is moved over said photosensitive surface to expose lines thereOn as a result of movement of said photoexposure device relative to said supporting surface, the path of light rays through said optical imaging system including at least one zone of non-parallel light rays, and an image rotator capable of rotating said non-parallel light rays, said image rotator being located in said zone of non-parallel light rays for rotating said image relative to said photosensitive surface, said image rotator comprising a Pechan prism having a plurality of surfaces fixed relative to one another for reflecting said light rays in such a manner that as said light rays pass therethrough their optical axis is first reflected away from and then eventually back to a given straight line, and means for rotating said Pechan prism about said given straight line, said Pechan prism having entrance and exit faces both of which faces are arranged perpendicular to the optical axis of the entering and departing light rays.
 4. A photoexposure mechanism for exposing lines on a photosensitive surface by means of a light spot moved thereover, said mechanis m comprising means defining a supporting surface surface, and a photoexposure device supported for movement relative to said supporting means in a plane generally parallel to said supporting surface, said photoexposure device comprising an aperture, means for illuminating said aperture, and an optical imaging system for forming an image of said aperture on said photosensitive surface which image is a substantially undistorted optical reproduction of said aperture and constitutes the afore-said spot which is moved over said photosensitive surface to expose lines thereon as a result of movement of said photoexposure device relative to said supporting surface, the path of light rays through said optical imaging system including at least one zone of non-parallel light rays, and an image rotator capable of rotating said non-parallel light rays, said image rotator being located in said zone of non-parallel light rays for rotating said image relative to said photosensitive surface, said image rotator comprising a reversion prism having a plurality of surfaces fixed relative to one another for reflecting said light rays in such a manner that as said light rays pass therethrough their optical axis is first reflected away from and then eventually back to a given straight line, and means for rotating said reversion prism about said given straight line, said reversion prism having entrance and exit faces both of which faces are arranged perpendicular to the optical axis of the entering and departing light rays.
 5. A photoexposure mechanism for exposing lines on a photosensitive surface by means of a light spot moved thereover, said mechanism comprising means defining a supporting surface for supporting a piece of material having a photosensitive surface, and a photoexposure device supported for movement relative to said supporting means in a plane generally parallel to said supporting surface, said photoexposure device comprising an aperture, means for illuminating said aperture, and an optical imaging system for forming an image of said aperture on said photosensitive surface which image is a substantially undistorted optical reproduction of said aperture and constitutes the afore-said spot which is moved over said photosensitive surface to expose lines thereon as a result of movement of said photoexposure device relative to said supporting surface, the path of light rays through said optical imaging system including at least one zone of non-parallel light rays, and an image rotator capable of rotating said non-parallel light rays, said image rotator being located in said zone of non-parallel light rays for rotating said image relative to said photosensitive surfaces, said image rotator comprising a prism having a plurality of surfaces fixed relative to one another for reflecting said light rays in such a manner that as said light rays pass therethrough their optical axis is first reflected away from and then eventually back tO a given straight line, and means for rotating said prism about said given straight line, said prism having entrance and exit faces both of which faces are arranged perpendicular to the optical axis of the entering and departing light rays, said photoexposure device including a first support member to which said prism is fixed, a second support member, means attaching said first support member to said second support member and permitting said first support member to be manually adjusted relative to said second member to shift said first support member toward and away from said given straight line along a first line perpendicular to said straight line and to vary the inclination of said first support member relative to said straight line in the plane defined by said first line and said given straight line, a third support member, means attaching said second support member to said third support member and permitting said second support member to be manually adjusted relative to said third member to shift said second support member toward and away from said given straight line along a second line perpendicular to both said given straight line and said first line and to vary the inclination of said second support member relative to said given straight line in the plane defined by said second line and said given straight line, and a main frame, said means for rotating said prism including means mounting said third support member to said main frame for rotation relative to said main frame about said given straight line.
 6. A photoexposure device as defined in claim 5 further characterized by said third support member being a barrel member having its axis generally aligned with said given straight line, and two bearings located respectively at opposite ends of said barrel member for rotatably supporting said barrel member relative to said main frame, said first support member, said second support member and said prism being located within said barrel member generally between said two bearings. 